He was accompanied by his parents, brother, sister and a medical escort for the journey, to spend the "last days of life" with relatives in Argentina, his mother, Andrea Lopez said.

Their first flight landed one hour late at 9pm and they were not able to make the second plane, despite having around 90 minutes to get from Terminal 3 to Terminal 5.

Ms Lopez said the group had to wait 45 minutes even before they could leave the first plane, with BA cabin crew telling them there was a problem with an airport lift.

Nahuel, who suffers from an incurable disease that mainly affects the brain and spinal cord, was eventually given a "very narrow and uncomfortable wheelchair", his mother said.

Instead of then being taken to the second plane, she claimed they were left in a corridor at Terminal 3 for several hours.

Ms Lopez said: "W e were supposedly going to be moved to the second plane. But the time was passing and this never happened.

"We were really concerned about losing the flight and the airport staff just kept telling us that they knew nothing about this second flight as they were 'only' the wheelchair men.

"We tried once, and once again, to convince them to make the proper phone calls for transferring us to Terminal 5 as soon as possible, but again nothing happened and we stayed at the corridor of the airport absolutely locked and blocked without any chance to do anything.

"Our sick son started to moan and show evident signals of tiredness and discomfort, as well as our other two children."

Nahuel's condition means he cannot stay in a seated position for long periods of time, so he was laid on the floor and seen by a paramedic.

His parents repeatedly complained about the situation "without any valid response form the airport staff", Ms Lopez said.

She added that a member of staff from BA eventually came to their assistance in the early hours of the morning to arrange for them to move to a hotel close to the airport and rebook their flights.

They were able to fly to Argentina 24 hours later than planned.

A Heathrow spokeswoman said: "This is clearly a distressing time for Nahuel's family, for which we are sorry.

"From our initial investigations, we understand Nahuel's own wheelchair was not available once he left the aircraft and he was uncomfortable in the replacement wheelchair.

"On the advice of the medical staff travelling with him, he was temporarily laid down on the floor. Heathrow arranged for a paramedic to attend him.

"After a discussion with Nahuel's relatives and medical staff he was transported to a local hotel by the London Ambulance Service before travelling out the next day.

"We continue to work with all parties involved to find out all the detail of what happened and how his journey could have been made more comfortable."

A BA spokeswoman refused to comment on whether Nahuel had travelled with his own wheelchair.

She said: "We understand this must have been a very upsetting time for the family. We provided hotel accommodation for Nahuel and his carer to make them as comfortable as possible, and booked them on to the next available flight to get them home as quickly as we could.

"We arranged for a doctor to provide suitable food during his stay and provided a temporary wheelchair to get him to and from the aircraft.

"We continue to investigate with the wheelchair provider and Heathrow."